Like [MENTION=152773]noglider[/MENTION] says, it's an easy swap, and the weight change is insignificant. For every tooth that you add to the cog, the axle has to move forward by approximately half the tooth spacing, or 1/4 inch. If you add two teeth, then you can put the axle back to its original position by adding a link to the chain. So it makes sense to add an even number of teeth, to keep the axle in its original position, unless your dropout slots are long enough to have plus or minus 1/4 inch to play with.

On one of my bikes, I had to choose my teeth carefully because the dropout slots don't have that much give or take once the length of the anti-rotation washers is factored in. I didn't want the washers to overhang the slots, though I don't know if that's a terrible thing, I tend to trust myself when something just doesn't seem right.

That's the calculus of IGH cogs as I understand it. Niagara Cycle has a range of sizes that fit Sturmey Archer. I don't know if Shimano uses the same inside diameter.

It depends on what it is called, and that varies. I would probably call that a striaght bar road bike. Some people call it a hybrid. Happens on lots of things.

I've got this Save up to 60% off Avid Disc Brake SRAM Apex Cyclocross | Cross Bikes - Motobecane Fantom Cross which is the same frame. Mine has the carbon fork, though. With all my lights, 2 full water bottles + plastic cages, Shimano PD-M424 pedals, a Conti Gatorskin (700 x 32c) in the front, and a Conti Touring Plus Reflex (700 x 32c) in the back. It is 27 lbs.

20 gears seems to be plenty (46-36 double crankset, 11-32 cassette) for my commute of 30 miles round trip with 600 feet of climbing on the way home. I'm probably going to switch out the chain rings for a true, compact double of 50-34 to get better separation of gears and more low end, but that's just because I have other climbs I want to do. For your needs, the cyclocross crankset should be sufficient.

The Fantom is very rideable, and the geometry isn't so aggressive that it's really difficult to get the bars even or above the level of the seat if you need the higher bars for your back. It's nice having the option of getting in the drops in the wind too.

More on the bike making a difference - here's my quick history of commuter bikes. I just started bike commuting in Spring 2013. You'll see I end up where some others in this thread have suggested - on an older steel road bike.

1. Old department store full-suspension mountain bike with knobbies that had hung on my garage ceiling for years. Heavy and slow. I had to get off and push it up one hill on my first day. I wasn't all that fat, but quite out of shape from sitting behind a desk and driving to work for many years.

2. I found this forum.

3. Bought a '90s rigid mountain bike from craigslist. It came with knobbies. The lack of suspension and lighter weight made it feel very fast, indeed.

4. Put the knobbies on the shelf for future actual "mountain biking" and installed smooth street tires on the rigid mountain bike. The bike was MUCH faster on the street and hard-packed dirt trails. I couldn't imagine riding a faster bike. It FLEW...or so I thought.

And then...

5. A good friend who is coincidentally the same size as me got a new road bike and gave me his '90s steel road bike. I took it to a LBS for a full tuneup, new chain and cassette, bearings repacked, etc. Eventually I'll learn to do that stuff myself, but I had full-on bike fever by this point and wanted it done quickly and correctly, and I was also delighted to learn how relatively inexpensive bike maintenace is compared to car maintenance.

The road bike is pretty light and goes up hills practically effortlessly, compared to the rigid MTB with street tires. At first I thought I'd get out of shape again riding such a light bike that just rolls forever with so little effort, but of course that hasn't happened. I ride it more and for longer distances. It's wonderful, and I can't recommend a road bike highly enough.

Sorry for the long and self-indulgent post, but I was where you were about a year and a half ago and a light and fast steel road bike turned me into a out-of-control BIKE FANATIC. Why didn't I know cycling was so much fun before?

If I were you, I'd take the old Schwinn into a good LBS and have them do a complete overhaul. Keep the receipt. If you don't like it, put it on craigslist as "LIKE NEW CLASSIC ROAD BIKE! - PROFESSIONALLY REBUILT" or something and use the proceeds to help fund something you like even more.

I would go with a lighter bike and more gears etc first. I have about a 40 mile RT (18 north and 22 south) that was starting to wear me down and not be fun. I was going to go back to driving part way and riding the rest but on a whim I went into a e-bike shop. Started to look at them seriously, test rode a few and eventually I ended up with a Specialized Turbo S. It's made the commute fun again and knocked about an hour off the total time and it's the same time as if I drive part way. The e-bikes are not understood very well by most (at least in the US). It also saves enough energy so I can take my "real" bike on group rides on the weekend.

How is a complete overhaul going to make it go from being worse than my Windsor on a hill to better? Since granny gear on it is 39T by 28T it makes me question a road bike setup entirely... I think maybe I'll just mod the Windsor after all. :-/

EDIT: I should also mention the Schwinn's handlebars are bent from the previous owner, so that's another knock against it.

I think there are actually two separate issues here. One has to do with the bike, and the other has to do with expectations. You like your Oxford and the style of riding it lends itself to. Your previous commute was perfect for it, - short and relatively flat. You could get to work without much effort and no need to change clothes.

Though your new commute still isn't a terribly long one, it's a completely different kettle of fish. Regardless of what bike you use you're going to have to treat it accordingly. Getting you and any bike up hill is going to require some exertion. If the hills are long and steep enough, sweat is going to be part of the deal. You can decide how you manage that. For example, choosing some different clothing can prevent more of it from getting trapped next to your skin.

I do think lower gearing will help too, but in the end you still have to get to the top of the hills. There is no free lunch.

A few summers ago, I was climbing one of the few hills on my commute. It was hot and humid. I passed a woman wearing a light summery dress riding a cruiser/city bike. She could have been pulled right from the pages of "Cycle Chic" except that she was covered in sweat. It's not a look that I mind but I doubt it's what she intended. And of course I was sweaty too but a shower and change of clothes were waiting for me.